Nail fungus is an infection that's treatable. It's caused by a microscopic fungus that infects the surface under toenails and fingernails. Often, people have nail fungus without realizing it.

The fungi most likely to cause the problem are called dermatophytes. They are found in warm, damp areas throughout our environment. These include locker rooms, showers and swimming pools.

Normally, fingernails and toenails are good barriers to the fungus. They help prevent the fungus from invading the nail. Sometimes, however, the nail doesn't do its job. This can happen when there is untreated athlete's foot, a break in the nail from an injury, certain medical conditions or long-term exposure to dampness. Nail fungus then can invade the area under the nail.

When this happens, the fungi live under the nail in the nail bed and nail plate. The fungi actually eat protein in the nail called keratin. That causes thickened, yellowed nails and organic waste material to build up under the nail. Fungal infections also can force the nail to raise up from the nail bed.

When your nails look thickened and yellow, you probably keep them covered by shoes or by nail polish. You may stop doing some of the healthy activities you love.

You don't have to give up your gym workouts or beach and pool visits. Embarrassing nail fungus is a treatable infection.